1. Field of the Invention
The present invention relates to an electronic timepiece having a control circuit for a power source switch. Particularly, the present invention relates to an electronic timepiece capable of quickly starting a clock circuit when power is supplied, during inspection, in the middle of an assembly process.
2. Description of the Related Art
An electronic timepiece, particularly a rechargeable electronic timepiece, can use a small-capacity capacitor and a large-capacity capacitor in some cases. In this case, the small-capacity capacitor is used to operate a clock circuit of the electronic timepiece until the large-capacity capacitor is charged to a level at which the large-capacity capacitor can normally operate the clock circuit of the electronic timepiece. When a voltage detecting circuit detects that the large-capacity capacitor is sufficiently charged, the power source, to supply power to the electronic timepiece is switched from the small-capacity capacitor to the large-capacity capacitor. When a voltage of the large-capacity capacitor drops, the power source for supplying power to the electronic timepiece is switched from the large-capacity capacitor to the small-capacity capacitor (refer to Japanese Patent Application Unexamined Publication No. 4-81754, FIG. 1 on page 5).
In general, this type of rechargeable electronic timepiece has a solar cell or the like as a power source, and charges the large-capacity capacitor and the small-capacity capacitor using this solar cell as the power source. However, during the assembly process in a plant or during the disassembly and cleaning at a retail shop, it is often necessary to confirm the operation of the clock circuit before the solar cell before the power source is built into or restored to the electronic timepiece. In this case, the large-capacity capacitor (usually a secondary cell) not connected to the solar cell is built into the electronic timepiece, thereby operating the clock circuit by using the power charged in this large-capacity capacitor.
A conventional technique is explained below with reference to FIG. 15. FIG. 15 is a block diagram of a conventional rechargeable electronic timepiece. In FIG. 15, a reference numeral 1 denotes power generating means, which is a solar cell according to the present conventional example. A reference numeral 2 denotes first storage means that stores energy of the power generating means 1, and operates a clock circuit. A capacitor is used for the first storage means, according to the present conventional example. A reference numeral 3 denotes second storage means that stores energy of the first power generating means 1, and discharges energy to the first storage means 2 when the power generating means 1 is not generating power. A secondary cell is used for the second storage means, according to the present conventional example. In general, a cell having a smaller capacity than that of the secondary cell 3 is used for the capacitor 2.
Reference numerals 4 and 5 denote backflow preventing diodes that prevent a backflow of the energy stored in the first storage means 2 and the second storage means 3 to the power generating means 1, when the power generating means 1 is not generating power, or when the power generating means 1 is not generating electromotive force. A reference numeral 6 denotes a switch for turning on so as to charge power generation energy of the power generating means 1 to the second storage means 3. This switch 6 consists of an N-channel transistor 61, according to the present conventional example. A reference numeral 7 denotes a switch to connect the first storage means 2 and the second storage means 3, in parallel, when the second storage means 3 is sufficiently charged. According to the present conventional example, the switch 7 consists of a backward N-channel transistor 71 and a forward N-channel transistor 72.
A reference numeral 8 denotes a clock circuit. The clock circuit 8 includes: an oscillating circuit 81; an oscillation halt detecting circuit 82 that detects whether the oscillating circuit 81 is oscillating; a frequency-dividing circuit 83 that divides a frequency of a signal of the oscillating circuit 81; a waveform shaping circuit 84 that generates a desired signal using a signal of the frequency-dividing circuit 83; and a cell voltage detecting circuit 85 that detects a voltage of the second storage means 3. The clock circuit 8 also includes a digital frequency controlling circuit and a motor driving circuit, which are omitted from the present explanation.
The operation of the conventional rechargeable electronic timepiece shown in the block diagram in FIG. 15 is explained next. When the second storage means 3 is not sufficiently charged, the cell voltage detecting circuit 85 detects that the voltage of the second storage means 3 is low, and turns off the switch 7. The waveform shaping circuit 84 controls the switch 6 to be repeatedly turned on and off every second. While the switch 6 is off, the power generation energy of the power generating means 1 is charged to the first storage means 2. While the switch 6 is on, the power generation energy of the power generating means 1 is charged to the second storage means 3.
When the voltage of the second storage means 3 rises after the second storage means is charged by the power generating means 1 when the second storage means 3 is not sufficiently charged, the cell voltage detecting circuit 85 detects the rise of the voltage of the second storage means 3, and turns on the switch 7. As a result, the first storage means 2 and the second storage means 3 are connected in parallel. Therefore, the power generating means 1 simultaneously charges the first storage means 2 and the second storage means 3, regardless of whether the switch 6 is on or off. In the state that the first storage means 2 and the second storage means 3 are connected in parallel, the second storage means 3 replenishes energy to the first storage means 2 even when the power generating means 1 does not generate power. Therefore, the clock circuit 8 can continue in operation.
When a state that the power generating means 1 does not generate power continues, the energy stored in the second storage means 3 decreases. Then, the cell voltage detecting circuit 85 detects a reduction in the voltage of the second storage means 3, and turns off the switch 7. As a result, the power source of the clock circuit 8 is switched to the first storage means 2. When the state that the power generating means 1 does not generate power further continues, the energy stored in the first storage means 2 is consumed, which lowers the voltage, and halts the operation of the oscillating circuit 81. At the same time, the waveform shaping circuit 84 halts the operation, and the switch 6 is turned off.
When the state that the power generating means 1 does not generate power further continues, the energy stored in the first storage means 2 further decreases due to a leakage inside the clock circuit 8 or the like, and the voltage of the first storage means 2 comes close to 0 volt (GND). Then, there is a risk that a potential of an L level, that the waveform shaping circuit 84 and the cell voltage detecting circuit 85 are outputting to turn off the switch 6 and the switch 7, is recognized as an H level, and the switch 6 and the switch 7 are turned on. In order to avoid this risk, the waveform shaping circuit 84 and the cell voltage detecting circuit 85 are configured to output the L level of a bulk potential of respective N-channel transistors, thereby turning off the switches, while the oscillation halt detecting circuit 82 is detecting the oscillation halt.
As explained above, when the clock circuit 8 has halted the operation, the switch 7 is in the off state, and the power source of the clock circuit is set to the first storage means 2. Therefore, the clock circuit 8 starts operating again when energy is stored in the first storage means 2, that is, when the power generating means 1 starts power generation. Because the switch 6 and the switch 7 are in the off state, when the power generating means 1 starts generating power, the power energy generated by the power generating means 1 is stored into the first storage means 2. When the voltage of the first storage means 2 exceeds the operating voltage of the oscillating circuit 81, the oscillating circuit 81 starts operating, and the switch 6 and the switch 7 can be controlled.
The above explains the operations of the power generating means 1 and the first and the second storage means 2 and 3, in the state that the power generating means (i.e., the solar cell) 1 is connected to the circuit. However, as explained above, it is often necessary to confirm the operation of the clock circuit before the power generating means 1 is connected to the first storage means 2 or the second storage means 3 in the middle of the assembly process in the plant.
In this case, at the beginning, the second storage means 3 that is charged to some extent beforehand is put into the electronic timepiece (i.e., connected to or built in the circuit of the electronic timepiece). Before the power generating means 1 is connected to the circuit, the clock circuit 8 is in a non-driven state as a matter of course. When the second storage means 3 is input to the electronic timepiece, it becomes possible to charge the first storage means 2. However, because the clock circuit 8 is not operating, the cell voltage detecting circuit 85 is in the non-driven state. Therefore, the first storage means 2 as the power source of the clock circuit 8 is separated from the second storage means 3. To overcome this difficulty, both sides of the switch 7 are connected with a conductive pin to compulsively charge the first storage means 2, thereby driving the clock circuit 8. As an alternative method, it is necessary to take the trouble of connecting the power generating means (i.e., the solar cell) 1 to the circuit to secure a power source, thereby driving the clock circuit 8. According to the above method, when the voltage of the first storage means 2 becomes equal to or higher than a constant voltage, the clock circuit 8 starts operating. Thereafter, the operation of the clock circuit is confirmed. For example, the power consumption is checked.
As described above, the conventional chargeable electronic timepiece has the following problems.
When the cell voltage of the first storage means 2 is insufficient, the first storage means 2 must be charged to operate the clock circuit 8. For example, in order to confirm whether the clock circuit 8 operates in the middle of the assembly process of the production line in the plant, it is necessary to (1) compulsively charge the first storage means 2 by putting the second storage means 3 into the electronic timepiece, or (2) charge the first storage means 2 by connecting the power generating unit (i.e., the solar cell) 1 to the circuit.
Particularly at the time of measuring power consumption of the clock circuit 8 in the production line, an ammeter is usually connected to a terminal of the second storage means 3. However, the clock circuit 8 does not operate until when the first storage means 2 as the power source of the clock circuit 8 is charged. Therefore, it is necessary to take the trouble to compulsively charge the first storage means 2. To take time in charging the first storage means 2 in this way is very troublesome. This point similarly applies to the disassembly and repair of the electronic timepiece.